Brakes go flat at end of day

[wunderbra]

Helping a friend here.

Her 93 Postal wagon (RHD), has a brake problem. Near the end of her daily run, after 700 stops, the brake pedal will just go to the floor.

New Subaru master cylinder, brake fluid flush- still same thing.

I'm thinking some kind of heat related problem ( from CAT) but dunno.

Anyone ever heard of this?

[evolegacy]

does she lose brake fluid at all? if so, ever checked the brake lines? could be a punctured/ruptured line somewhere and its causing her to lose pressure in the system

[wunderbra]

No fluid loss at all. That would have been easy.

[jey]

What kind of brake pads are being used and what is the condition of them?

[wunderbra]

Subaru OEM pads. Rears are pretty thin. Fronts are fine.

[Airgne]

any wet look around the piston area on the calipers?

also the pads might be getting glazed over from the non stop stopping.

[httrdd]

Wow I am actually puzzled. Seems that there has to be a problem with hydraulics somewhere.

[Huffer]

Brake lines. The old brake lines are probably worn out and flex too much.

[wunderbra]

I am puzzled as well. Front pads are good. No leaks anywhere. The brakes work fine for hours then.. flat!
If the lines were flexing too much, the pedal would be soft to start with..imo.

It is a very hard problem to duplicate, since it takes about 700 stops before it happens.
This postal wagon has been running this route for years, with no brake problems.

[Huffer]

Not necessarily. Brake fluid heats up, and brake lines heat up. The lines might be at the point where they don't flex until they're at a certain temp for extended periods of time.

[StatGSR]

Also, how old is the brake fluid? Fluid itself could be so old and crappy that it boils by the end of the day.

[jey]

Also, how old is the brake fluid? Fluid itself could be so old and crappy that it boils by the end of the day.

Read the original post:


New Subaru master cylinder, brake fluid flush- still same thing.

That said, are you sure all the old fluid was flushed out when it was done? A mix of old stuff is almost as bad as having the old stuff in there.

[decke48]

sounds like heat issues. still using dot 3 fluid? could be after so many stops the fluid heats up to much and air-ates, or theres hydraulic issues, cheapest thing is to flush with a dot 4 or 5 fluid, if it persists youll need to look at hoses/lines and calipers for problems

[Okin DaVanh]

sounds like heat issues. still using dot 3 fluid? could be after so many stops the fluid heats up to much and air-ates, or theres hydraulic issues, cheapest thing is to flush with a dot 4 or 5 fluid, if it persists youll need to look at hoses/lines and calipers for problems


This.




And try swapping out those rear shoes. A balanced brake system is what it is... balanced.

[ScaryFatKidGT]

Well idk how much money you wanna throw at it it sure seems like a leak to me or boiling fluid but maybe some ATE brake fluid (its almost the same price and stock crap and a lot better), SS brake lines or maybe just new OEM ones, the ones that are on it are probably stock from 1993! and some performance pads for the front? Hawk or Axxis again there about the same price as premium OEM replacement pads.

With all that she should be able to do her route twice as fast with out brake fade! lol

Another suggestion is to have her take a coffee brake or something about 3/4 of the way through her run to let the brakes cool if this fixes it then do the mods I suggested if not maybe shes going through some Subaru brake Bermuda Triangle? lol

[ScaryFatKidGT]

or you could have a seized caliper thats causing things to over heat?